The present invention relates to rolling-mill equipment, and more particularly to a device for automatic adjustment of the roll gap in a mill stand.
The invention is best suited for adaptation in rolling mills for strips or sheets of metal.
There is known in the art a device for automatic adjustment of a roll gap in a mill stand, comprising one-chamber hydraulic cylinders adapted for prestressing the mill stand and mounted under the bottom roll chocks.
The hydraulic cylinders are provided with an electrohydraulic system to control the pressure of a fluid (oil) being fed into said hydraulic cylinders from a high-pressure fluid source.
The aforesaid eletrohydraulic system comprises electric load cells to absorb a rolling force, electric loads cells for registering a mill stand prestressing force and servovalves adapted to regulate the pressure of the fluid flow fed into the hydraulic cylinders for prestressing the mill stand, the servovalves having their own electric control circuit.
The electric load cells for absorbing the rolling force are installed under the stand housing screws and on the top roll chocks.
The electric load cells for registering the mill stand prestressing force are installed between a top-housing separator and the bottom roll chocks.
The servovalves together with their electric control circuit and the high-pressure fluid source are disposed outside the mill stand.
The afore described device for automatic adjustment of a roll gap in the mill stand operates as follows.
While rolling a metal strip, the rolling force changes and is then registered by said electric load cell.
The signal from this load cell is applied to the electrohydraulic system for fluid pressure control in the hydraulic cylinders.
As a result, the servovalve is operated to alter the fluid pressure in the hydraulic cylinder thereby altering the stand prestressing force.
It is, therefore, by way of effecting the prescribed alteration of the stand prestressing force in accordance with the rolling force that the automatic adjustment of the mill roll gap within the preset range is assured.
The aforesaid prior-art device allows for substantially accurate adjustment of a roll gap in the mill stand.
It is to be understood, however, that the servovalves require a highly purified fluid (oil), and, should it be otherwise, they become unstable in operation and the device looses its operating dependability.
In addition, the servovalves are rather complex in design, expensive to manufacture and difficult to operate. The servovalves, as well as their electric control system, require attendance of highly qualified personnel.
Inventor's Certificate of the USSR No. 452380 teaches a device for automatic adjustment of a roll gap in a mill stand, comprising at least one hydraulic load cell at both sides of the mill stand intended for absorbing a rolling force and mounted under the chocks of one of the rolls.
To develop a stand prestressing force, the device is provided with hydraulic cylinders mounted separately on both sides of the stand so as to have no effect on the load cells.
To regulate the fluid (oil) pressure in the hydraulic cylinders, the device is provided with three-chamber fluid pressure regulators, one for each load cell, communicating through the first end chamber thereof with chambers of the hydraulic cylinders at the respective side of the mill stand. Said fluid pressure regulator communicates through its midchamber with the load cell chamber by way of a shutoff valve, and through its second end chamber the regulator communicates with a constant-pressure fluid source.
The aforesaid prior-art device functions in the following manner.
During the rolling operation, as a metal strip passes between the rolls, the fluid pressure in the load cells varies with the rolling force.
Accordingly, the fluid pressure changes in the midchambers of the three-chamber pressure regulators thereby resulting in a shift of the valve spools of the pressure regulators.
The shifting of the valve spools causes the fluid pressure in the hydraulic cylinders to change, which results in the change of the stand prestressing force.
The device parameters are preselected so as to provide for the automatic adjustment of the mill roll gap by varying the stand prestressing force in accordance with the rolling force in a predetermined range. As to the control range, it is determined by way of adjusting the shutoff valve in accordance with a fluid pressure in the constant-pressure fluid source.
However, during the valve spool displacement in the three-chamber pressure regulators, there occurs an overflow of fluid from the load cell chamber into the mid-chamber of the three-chamber pressure regulator, which results in the displacement of the roll chocks thereby adversely affecting the accuracy of the roll gap adjustment.
Accordingly, it is an object of the present invention to provide a device for automatic adjustment of a roll gap in a mill stand, which will be simple in construction, reliable in operation and inexpensive to manufacture.
Another object of the invention is to provide a device for automatic adjustment of a roll gap in a mill stand, which will enable the use of a fluid (oil) with a purity degree characteristic of that employed in conventional hydraulic drives.
Still another object of the invention is to provide a device for automatic adjustment of a roll gap in a mill stand, which can be readily serviced by attendants of ordinary skill.
These and other objects and features of the invention are accomplished by the provision of a device for antomatic adjustment of a roll gap in a mill stand comprising two similar parts operating on an identical principle and arranged on each side of the mill stand, said operable parts each incorporating at least a one-chamber load cell mounted under a support member of one of the working rolls and adapted to absorb a rolling force; hydraulic cylinders mounted between a backup member of another working roll and a roll housing so as to have no effect on the load cell, said cylinders being intended for prestressing the mill stand, a three-chamber fluid pressure regulator communicating through its first end chamber with chambers of the hydraulic cylinders, through its mid-chamber with the load cell chamber, and through its second end chamber with a constant-pressure fluid source arranged outside the mill stand, said source being at least one of two operable parts of the device. In accordance with the invention, the device is provided with regulated pressure valves, one for each load cell, a throttle chamber of said pressure valves communicating with an alternating-pressure fluid source, one for each operable part of the device, and arranged on two sides of the mill stand, and with a mid-chamber of the three-chamber fluid pressure regulators, a control chamber of said valves communicates with chambers of the load cells.
In the device of the invention a change in the rolling force results in a change of the fluid pressure in the load cell and at the same time in the hydraulic cylinder chamber being in direct communication therewith.
As a result of this change, a valve spool of the regulated fluid pressure valve is shifted thereby to alter the direction of the fluid flow now passing through the throttle chamber of the regulated pressure valve, while a pump, being in direct communication with said chamber, now pumps the fluid into the mid-chamber of the three-chamber pressure regulator.
The valve spool of the three-chamber fluid pressure regulator is shifted thereby to alter the fluid pressure in the hydraulic cylinders for prestressing the stand, said cylinders being also in communication through chambers thereof with the first end chamber of the pressure regulator.
This brings about a change in the stand prestressing force and, consequently, a change in the roll gap.
Thus, it is through a proper selection of parameters for the hydraulic cylinders the load cells, the regulated pressure valve and the three-chamber pressure regulator, that there is attained, like in the prior-art devices, a prescribed variation in the stand prestressing force depending on the change in the rolling force, thereby enabling automatic roll gap adjustment.
Furthermore, there comes into play the rolling force produced during the rolling operation, which causes fluid to pass from the load cell into the control chamber of the regulated pressure valve with a spool thereof being of far less diameter than that of the load cell piston rod. The spool traverse being rather limited, the fluid from the load cell is prevented from flowing into the mid-chamber of the three-chamber pressure regulator thereby rendering immobile the roll chock resting upon the load cell piston rod.
It is expedient that the regulated pressure valve be combined with the three-chamber pressure regulator so that the midchamber of the regulator will serve as a control chamber of the regulated pressure valve, and the first end chamber of the pressure regulator will serve as a throttle chamber of the regulated pressure valve. This will substantially simplify the design of the proposed device.
During the rolling operation, the fluid is fed to the hydraulic cylinders for prestressing the mill stand directly from the constant-pressure fluid source. Such delivery of fluid precludes the use of a number of units and lines in the device of the invention, and makes it simpler and more reliable in operation.
It is also advisable that the proposed device be provided with means for varying the amount of fluid in a closed chamber formed during the rolling operation by the first end chamber of the pressure regulator and by the chambers of the hydraulic cylinders at the respective stand side, said means being made as a hydraulic cylinder fitted with a screw rod and having its working chamber in communication with the closed chamber.
The aforesaid means are designed to allow parameter correction to be effected in the proposed device with the stand rigidity being varied, whereby said device is rendered easier in operation.
In accordance with the concepts of this invention, there is provided a device for automatic adjustment of a roll gap in a mill stand, which is simple in construction, inexpensive to manufacture, and enables the use of a fluid (oil) with a purity degree characteristic of that employed in conventional hydraulic drives, said device being easy in operation and readily serviceable by attendants of ordinary skill.